Crossover performance of power amplifier
There is provided an amplifier arrangement comprising: a main amplifier connected to receive an input signal and generate an amplified version of the input signal; an additional amplifier, having a smaller geometry than the main amplifier, connected to receive the input signal and generate an amplified version thereof; and wherein the outputs of the main amplifier and the additional amplifier are combined to provide an amplified output.
1. An amplifier arrangement comprising:
a main push-pull amplifier, including a first transistor and a second transistor, and connected to receive an input signal and generate an amplified version of the input signal; and
an additional amplifier, connected to receive the input signal and generate an amplified version thereof;
wherein the outputs of the main amplifier push-pull amplifier including the first and the second transistors and the additional amplifier are combined to provide an amplified output, and
wherein during operation in a crossover region of the main push-pull amplifier including the first and the second transistors, the bandwidth of the additional amplifier is greater than the bandwidth of the main push-pull amplifier including the first and the second transistors.
2. The amplifier arrangement of claim 1 , wherein the additional amplifier comprises a push-pull amplifier.
3. The amplifier arrangement of claim 1 , wherein during operation in the crossover region of the main push-pull amplifier including the first and the second transistors, the bandwidth of the main push-pull amplifier including the first and the second transistors is reduced compared to the bandwidth of the main push-pull amplifier including the first and the second transistors during operation outside the crossover region.
4. The amplifier arrangement of claim 1 , wherein during operation when the bandwidth of the main push-pull amplifier including the first and the second transistors is reduced, the bandwidth of the additional amplifier is greater than the bandwidth of the main push-pull amplifier including the first and the second transistors.
5. The amplifier arrangement of claim 1 , wherein during operation when the bandwidth of the main push-pull amplifier including the first and the second transistors is reduced, the bandwidth of the additional amplifier is maintained at a level corresponding to the bandwidth of the main amplifier before the bandwidth of the main amplifier was reduced.
6. The amplifier arrangement of claim 1 , wherein the bias current of the main push-pull amplifier including the first and the second transistors is set in dependence on a level of bias current required to provide a required bandwidth outside a crossover region of operation.
7. The amplifier arrangement of claim 1 , wherein the bias current of the main push-pull amplifier including the first and the second transistors is set in dependence on a level of bias current to achieve a desired bandwidth of operation with an output transistor of the push or pull side of the amplifier fully turned on.
8. The amplifier arrangement of claim 1 , further comprising a high pass filter connected to receive the input signal and provide a high pass filtered version of the input signal as the input to the additional amplifier.
9. The amplifier arrangement of claim 1 , wherein the additional amplifier increases the overall bandwidth of the amplifier arrangement, during a period in which the bandwidth of the main push-pull amplifier including the first and the second transistors is reduced, such that the phase shift between the input and the output is reduced relative to the phase shift between the input and output of the main amplifier.
10. The amplifier arrangement of claim 1 , wherein the additional amplifier increases the overall bandwidth of the amplifier arrangement, during a period in which the bandwidth of the main push-pull amplifier including the first and the second transistors is reduced, such that the bandwidth of the main push-pull amplifier including the first and the second transistors is reduced relative to the bandwidth of the main push-pull amplifier including the first and the second transistors without the additional amplifier, wherein the bias current of the main push-pull amplifier including the first and the second transistors is reduced relative to the bias current of the main amplifier without the additional amplifier.
11. The amplifier arrangement of claim 1 , wherein the main amplifier is a power amplifier.
12. The amplifier arrangement of claim 1 , wherein the main push-pull amplifier including the first and the second transistors comprises a current mirror arrangement for driving an output transistor.
13. The amplifier arrangement of claim 1 , wherein the main push-pull amplifier including the first and the second transistors and the additional amplifier are provided on an integrated circuit, and the output of each amplifier is connected to a respective bond wire of the integrated circuit.
14. A method of amplifying an input signal comprising:
amplifying the input signal in a main push-pull amplifier including a first transistor and a second transistor, and generating an amplified version of the input signal;
amplifying the input signal in an additional amplifier to generate an amplified version thereof; and
combining the amplified versions of the input signal to provide an amplified output,
wherein during operation in a crossover region of the main push-pull amplifier including the first and the second transistors, the bandwidth of the additional amplifier is greater than the bandwidth of the main push-pull amplifier including the first and the second transistors.
15. The method of claim 14 , further comprising the step of providing a bias current for the main push-pull amplifier including the first and the second transistors determined in dependence on a predetermined bandwidth of operation of the main amplifier.
16. The method of claim 15 , wherein in any region of operation of the main push-pull amplifier including the first and the second transistors, for the determined bias current, where the bandwidth of operation of the main push-pull amplifier including the first and the second transistors is reduced, the bandwidth of operation of the additional amplifier provides for full bandwidth operation.
17. The method of claim 15 further comprising a bias current for the additional amplifier which is less than the bias current for the main push-pull amplifier including the first and the second transistors, determined in dependence on a predetermined bandwidth of operation for the additional amplifier which corresponds to the bandwidth of operation of the main push-pull amplifier including the first and the second transistors.
18. The method of claim 15 , wherein the bias current of the main push-pull amplifier including the first and the second transistors is reduced compared to the bias current required for the main push-pull amplifier including the first and the second transistors if the additional amplifier was not provided.
19. The method of claim 14 , wherein the main push-pull amplifier including the first and the second transistors is a push-pull amplifier including complementary output transistors, wherein the bias current is determined in dependence on the bias current required to achieve the predetermined bandwidth with either output transistor turned on.
20. The method of claim 14 , wherein the main push-pull amplifier including the first and the second transistors and the additional amplifier are provided on an integrated circuit, the method further comprising connecting the output of each amplifier to a respective bond wire of the integrated for connection off-chip.